The invention relates generally to the field of force feedback mechanisms. In particular, this invention relates to a motor-driven feedback mechanism for providing feedback to a vehicle operator.
Modern vehicular braking systems utilize brake-by-wire technology rather than hydraulic systems. In pure hydraulic braking systems, depressing the brake pedal actuates a piston in a hydraulic master cylinder. The movement of the piston in the master cylinder compresses the brake fluid which transfers the pressure to the brakes of the vehicle, typically through a booster operated by the engine vacuum. The operator receives hydraulic feedback in the form of resistance at the pedal input such as kickback and pulsations.
In a brake-by-wire system, the sensors on the brake pedal typically measure driver intent through force and displacement measurements. An electronic control unit receives signals from the sensors on the brake pedal and computes optimized braking forces. The electronic control unit signals electromechanical actuators on each wheel that apply the required pressure. No hydraulic lines are used, only electrical wires. Brake-by-wire systems provide numerous advantages including a reduction in weight, size and number of components necessary in the braking system. Electrical wiring is further more resistant to damage than hydraulic circuitry, and is more space-efficient. It is also easier to integrate advanced braking components such as ABS, traction and stability control elements via electrical systems rather than with traditional hydraulic braking systems. Typically, all that is necessary in such integrations is the addition of computer code to the electronic control unit.
Brake-by-wire systems are not without disadvantages. The most significant disadvantage is the lack of feedback of pedal resistance to the operator. Most operators appreciate this type of feedback and prefer to feel a more conventional pedal response such as kickback and pulsations upon application of the brakes. For this reason, it has become necessary to add pedal feel emulators to brake-by-wire systems to provide conventional pedal resistance. One such device is a stand-alone accumulator with movable pistons separated by a pair of springs. The springs provide improved pedal feel, but it has been noted that the feel is significantly different than conventional pedal systems.
U.S. Pat. No. 5,729,979 discloses a variable rate pedal feel emulator that improves pedal feel characteristics. Fluid is still used for semi-active pedal feedback in this mechanism, as well as a rubber spring modeled to simulate desired operator feedback.
It is desirable to further improve the feedback to an operator to make it more operator-adjustable and to further reduce the package and component size.
In one embodiment of the present invention, a motor-driven feedback mechanism for a braking pedal is provided. A pedal is linked to a shaft and a bi-directional motor capable of operating in a first and a second direction is linked to the shaft. A gearbox is driven by the bi-directional motor and the gearbox is attached to the shaft to effect rotation of the pedal. A motor controller is linked to the motor and a microprocessor capable of controlling the motor controller is linked to the motor controller. At least one sensor for measuring a parameter of the pedal and providing feedback to the microprocessor is provided.
In a second embodiment of the present invention, a motor-driven feedback mechanism is provided. A pedal is pivotally mounted to a frame via a shaft. A bi-directional motor capable of applying resistance to rotation and assistance to rotation of the pedal is provided. A means for measuring at least one parameter of the pedal and a means for analyzing at least one parameter of the pedal are provided. A means for controlling the bi-directional motor in order to adjust the speed and direction of rotation of the bi-directional motor in response to at least one measured parameter of the pedal is provided.
In a third embodiment of the present invention, a method for providing force feedback to an operator of a shaft-mounted pedal is provided. The method comprises the steps of measuring at least one parameter of a pedal pivotally linked to a frame and analyzing this parameter to determine operator intent. A motor controller is signaled and the direction of rotation and power of a motor is variably adjusted in order to provide mechanical assistance to rotation and assistance to rotation of the pedal and shaft.